Study On Clean Pulping And Bleaching Of Bamboo And Reaction Mechanism Of Oxygen-Containing Radical During Oxygen Delignification

With the rapid economic growth in China, there is a huge market demand for the paper and paper products. The limited forestry resources resulted in a severe shortage of wood pulp. Meanwhile, the unreasonable fiber raw material structure, small scale, poor facilities resulted in a serious environmental pollution which restricted the sustainable development of China's paper industry. On the other hand, China is one of the bamboo rich countries in the world and occupies the first place in amount of bamboo resource, the area and the accumulation of bamboo forest. Furthermore, the fiber and chemical composition of bamboo are suitable for pulping. Therefore, in order to utilize bamboo resource more effectively, lighten the pressure for wood fiber demand and reduce the pollution of paper industry, the extended modified continuous cooking (EMCC) and totally chlorine free (TCF) bleaching technologies and mechanisms of bamboo were studied in this thesis. The conditions of EMCC pulping and TCF bleaching were optimized; HO· and O2·^-generated in oxygen delignification process were determined and regulated; the changes of lignin structure during EMCC pulping and TCF bleaching were analyzed; the reaction mechanisms of O2·^- with lignin model compounds and cellulose model compounds were studied; which would provide the support for producing high quality bamboo pulp in technology and mechanism.Based on extended delignification principles, bamboo EMCC pulping was carried out to explore the effects of active alkali charge at the impregnating zone and current zone, warm white liquor concentration at the countercurrent zone, maximum temperature, sulfidity on pulping selectivity. The pulping selectivities of conventional and EMCC pulping were compared. It was found that EMCC process maintained a more even alkali concentration profile throughout the cook and a lower dissolved lignin concentration towards the end of cook with the alkali splitting charge and displacement of part of cooking liquors during the counter-current cooking stage, which allowed for lower cooking temperature, resulting in high pulping selectivity. To obtain lower Kappa number pulp, the pulp cooked by the higher cooking liquor concentration in the counter-current stage had better strength property than that by the higher maximum temperature. The optimal conditions of EMCC pulping at laboratory were: 14% (expressed as Na₂O) of active alkali charge at the impregnating zone and the current zone, 30 g/L of warm white...